This is what I did. The arms were extended 3 inches using butt welds. 1/4 inch thick gusset plates were welded on each side for a total of four plates. The vacant space in between the arms was boxed for strength.

Tom...maybe a curved bar-brace ahead of the tire and/or inside of the welded 'kinks'............otherwise......looking real good

Dennis,I'll be doing something like that once everything is in place to check clearances.

By the way Dennis, I'm also building a 250 motor to run in the M Class at Loring, Maine. Of course, if the motor is strong, it will bolt right into my A Class frame! Photo is attached of the frame without the motor.

This is what I did. The arms were extended 3 inches using butt welds. 1/4 inch thick gusset plates were welded on each side for a total of four plates. The vacant space in between the arms was boxed for strength.

Bo,Ditto the answer I gave to Dennis above. Making sure the tire clears the spring, and making sure the swingarm clears the frame where I've cut it just behind the foot peg mounts. Fitting a tube or shaped and boxed in plates inside the swingarm between the spring and the rear wheel would be most efficient.